"Despite the robust investment returns since 2004, annual growth in unfunded pension liabilities has outstripped these returns," Moody's warns in its latest report on the state of public pension systems. As Bloomberg reports, the 25 biggest systems by assets averaged a 7.45% return from 2004 to 2013, but liabilities tripled over the same period leaving them facing a $2 trillion shortfall as investment returns can't keep up with ballooning obligations. The top 25 funds account for 40% of the entire US public pension system with Illinois, Kentucky, Connecticut, and Louisiana at the top of the 'most underfunded' list.

As Bloomberg reports,

The 25 largest U.S. public pensions face about $2 trillion in unfunded liabilities, showing that investment returns can't keep up with ballooning obligations, according to Moody's Investors Service.